Belle's outfit is a jumper with a circle skirt; the white blouse has 3/4 sleeves and a spread collar. No socks or tights.
Alice's outfit is much more "little girl flouncy", with the short pouf sleeves and the peter-pan white collar on a dress with a gathered skirt, worn with tights.
To the casual onlooker, the key is always the hair. Belle's is brown and worn in a ponytail, and Alice is a blond, with that signature black "Alice band" holding it back off her forehead.